Data converters play a crucial rule in the electronics field as they bridge the analog world to the digital domain and vice versa in modern integrated circuits (ICs). Over the last decades, significant progress has been achieved in designing high resolution analog-to-digital converters (ADCs) and digital-to-analog converters (DACs). In order to characterize such sophisticated data converters, especially ADCs, spectral testing is now widely utilized. The spectral testing normally requires an input signal to the tested ADC having 3 to 4 bits more purity than the tested ADC itself. When the resolution of the ADC is high, for instance a 16-bit, it is very challenging (sophisticated circuitry design, and or complicated calibration) and costly to achieve a pure enough input signal. If the input signal does not meet the high purity requirement, the ADC output spectrum will no longer contain just ADC nonlinearity, but will also contain nonlinearity from the input signal. The ADC's specifications, such as total harmonic distortion (THD) and spurious free dynamic range (SFDR), cannot be accurately obtained from the output spectrum.
Accordingly, there remains a need for an improved signal generator design that provides ultra-pure sinusoidal/cosinusoidal signals with an easy implementation at a low cost.